Viral infections remain a considerable cause of morbidity and mortality. Despite advances in the availability of vaccines, the mechanisms of generating and maintaining effective antiviral immunity remains incompletely understood. A major concern in this regard is influenza virus, a focal point for a number of Projects in this Program. The vaccine for influenza virus must be remade each year because it has not yet been possible to generate broadly protective immunity to this rapidly evolving RNA virus and the potential emergence of devastating pandemic influenza virus strains remains ever present. Thus, it is essential that we understand the basic principles of long-term B cell and T cell immunity to viral infections, including influenza virus, to improve existing, and develop novel, vaccination strategies. A major complication with influenza virus infection is co-infection with bacteria resulting in bacterial pneumonia. It is unclear how such a co-infection with a virus and bacterial pathogen in the respiratory tract impacts antiviral immunological memory and future protective immunity to the virus. To address these questions, the research Projects will utilize common infectious agents. The overall goal of Core B is to generate, standardize, store and provide infectious agents to the Projects. In addition, Core B will optimize and validate assays to monitor the burden of infectious agents in tissues from infected animals. Thus, the specific Aims for this core are: 1) To define a model of respiratory infection with Streptococcus pneumonia (Sp) and coinfection with Sp and influenza virus;2) To generate and characterize Streptococcus pneumoniae expressing CD4 T cell determinant(s) from influenza virus HA;and 3) To produce, standardize, maintain and store infectious agents. The activities of this Core will therefore create synergy and interaction between the different Projects by creating a common and easily accessible set of tools, and by enhancing the quality, standardization and reproducibility of the data generated by the individual Projects.